I have both in my car well rather i have XM and my ipod…that being said i had the ipod long before i got XM an i thought it would be a waste but it was a gift, and i find that i use them equally.
Although in regards to sounds quality, being able to create your own playlists etc, XM or satelitte radio cant hold an Ipods jock strap… also the fact that you dont have to carry a case of cds is a nice bonus